Cultures of isolated adrenal medulla cells will be utilized to study various aspects of adrenal medulla function. Since the use of these cultures is relatively new we will first evaluate the effects of age in culture on the biochemistry, morphology, physiology and pharmacology of the cells. Once these cells are fully characterized investigations will be undertaken on the ionic requirements for stimulus-secretion coupling, the role of protein phosphorylation in secretion and possible roles of cyclic AMP and cyclic GMP in this process. The sites and mechanisms of action of drugs which inhibit secretion will be determined to enable their use to dissect out steps in the secretory process. The mechanisms by which stimulation causes short term activation of thyrosine hydroxylase as well as a long term induction of the enzyme will also be investigated. Factors such as availability of pterin co-factor, activity of monoamine oxidase and uptake and storage by the chromaffin vesicle which may affect the overall synthesis of epinephrine and norepinephrine will be evaluated and the possibility that epinine rather than norepinephrine is the natural precursor of epinephrine will be explored.